1. Field of the Invention
This invention relates generally to the field of digital video signal processing. More particularly, this invention relates to a method and apparatus for decomposing video signals utilizing analog to digital conversion.
2. Background of the Invention
In a number of existing color video systems such as the NTSC system used in the United States, the PAL system in use in much of Europe, the SECAM system used in France and custom or nonstandard systems, a composite video signal is used which contains both horizontal and vertical synchronizing pulses, both horizontal and vertical blanking pulses and video information. For color systems, these pieces of video information are normally encoded in order to achieve realistic color rendition. There are a number of ways of viewing the three pieces of information generally required for color video, but in each case information relating to brightness, hue and saturation may generally be derived. Brightness (luminance) relates to the position in which a particular color may be placed on a neutral gray scale. Hue relates to the specific color frequency which categorizes the color as red, green, blue, etc. Saturation is a measure of the degree of mixture of the color with white light so that a fully saturated color contains no white light and pastel colors contain relatively large amounts of white light.
The above information is primarily associated with the way in which the human eye interprets color. The information itself, however, can be encoded within a composite video signal in a number of possible ways. For example, the composite video signal may contain information on the relative content of each of three primary additive colors such as red, blue and green (or differential relationships among the three) or the signal maybe contain information about three subtractive primary colors such as yellow, cyan and magenta. In other techniques, actual luminance, saturation and hue information may be transmitted or, as is known in the art, chrominance, real illuminance and imaginary illuminance information or other types of information may be encoded in the composite video signal.
In any event, to achieve full natural color rendition, it is generally the case that at least three pieces of color information must be encoded into the composite video signal. If, however, less than full color spectral information is necessary, it is of course possible to only encode one or two pieces of such video information into the composite video signal.
In the field of image processing, a composite video signal often is decomposed into its constituent parts. If only a single field or frame of video is processed, then in some cases the real-time video aspects are relaxed and the system has a different architecture than would a real-time, full-motion video processing system.
Once the composite video signal is decomposed into its primary constituent parts, it can then be processed. The processing is often done in the digital domain where the analog video signal has been converted to a digital format. The digital processing of the video includes, but is not restricted to, a variety of operations such as:
"1. Compression, i.e. reduction of the number of bits to represent the image PA1 2. Image Enhancement PA1 3. Scene Decomposition PA1 4. Edge Detection PA1 5. Color Compensation PA1 6. Color Alteration PA1 7. Frequency Composition PA1 8. Correlation PA1 9. Optical Correction PA1 10. Gray Scale Segmentation PA1 11. Ghost Removal"
In order to perform any of a number of possible signal processing operations such as those above, it is desirable in many instances to be able to separate the color (or other) information from the composite video in order to individually manipulate each of the pieces of color information. This may be done by first simultaneously decomposing the three pieces of video information from the composite video signal and then converting that information to digital form for manipulation by a signal processing digital computer. The data after being manipulated can then be reassembled and converted back to analog information, if desirable, prior to display, transmission, etc.
One technique for accomplishing this is shown in FIG. 1 as system 10. In system 10, any one of a plurality of camera signals or other sources of composite video such as 12, 14, and 16 may be selected by an appropriate switch network 18 by selectively closing one of switches 18A, 18B or 18C. Switch 18 may be operated either by manual control or, as shown, by a control computer 20 which is responsive to a manual control panel 22.
An output 24 of switch network 18 provides a composite video signal to a decomposition network 25 (shown in broken lines) which may be represented as three separate decomposition networks 26, 28, and 30. In the example shown the composite video signal is decomposed into red, blue and green signals respectively. In addition, the composite video signal at output 24 is provided to synchronization detectors 32 which derive appropriate horizontal, vertical or other synchronization information from the composite signal and supplies that information to control computer 20 and decomposition networks 25 (26, 28 and 30).
Each of the decomposition networks 26, 28, and 30 respectively derive red, blue and green information from the composite video signal and applies that information to an input of one of three analog to digital converter circuits 34, 36 and 38. The outputs of each of these analog to digital converter circuits is coupled to a separate memory location wherein separate red, blue and green digital information is stored. Memory 40 may be representative of either three separate banks of memory in addition to various program memory, scratch pad memory, etc. or may also represent one larger bank of memory which is simply partitioned appropriately into separate memory segments 40A, 40B, 40C, and 40D wherein 40A contains red information, 40B contains blue information and 40C contains green information. Memory segment 40D may be used for program storage, scratch pad, etc. Memory segment 40D may be used by the control computer 20 and also by signal processing computer 42 for use in processing each of the individual red, blue, and green digital information. After the information has been processed, it may be desirable in some instances to convert the digital information back to analog using a digital to analog converter 44. Any digital signal can be used to derive the analog signal. A composite video signal may be derived by combining the red, blue and green and adding the appropriate control and synchronization waveforms before driving the analog to digital converter. This signal can be established and stored in memory segment 40D. The analog information may then be used to drive a CRT display or may be transmitted, etc.
By virtue of parallel processing utilizing three analog to digital converters 34, 36 and 38, the present system 10 may operate very rapidly to provide the necessary signal processing. However, such speed may be unnecessary when dealing with for example freeze frame types of video signals used for example in CAT scanning or teleconferencing wherein a single frame of video may be processed and transmitted. Also, since the cost of analog to digital converters is among the more expensive items in system 10, this system may be prohibitively expensive for some applications.